The high toxicity of nitrogen oxides and their role in the formation of acid rain and tropospheric ozone have resulted in the imposition of strict standards limiting the discharges of these chemical species. To meet these standards, it is generally necessary to remove at least part of these oxides present in the exhaust gases from stationary or mobile combustion sources.
Denitration or selective catalytic reduction (SCR) technology is commonly applied to combustion-derived gases for removal of nitrogen oxides. Denitration comprises the reaction of nitrogen oxide species in the gases, such as nitric oxide (NO) or nitrogen dioxide (NO2), with a nitrogen containing reductant, such as ammonia or urea, resulting in the production of nitrogen gas (N2) and water.
SCR catalytic reactors generally comprise honeycomb structural catalyst bodies containing fluid flow paths that enable contact between flue gas streams and catalytically active components of the honeycomb bodies. The structure of a modular catalytic reactor is typically composed of one or more catalytic layers with each layer comprising a large number of modularized sections. Each modularized section further comprises a metal support framework which holds an assembly of honeycomb catalyst bodies in place wherein non-bonding, compressible packing materials between the catalyst bodies are used for proper flow distribution of fluid streams passing through the catalyst bodies.
Honeycomb SCR catalyst bodies are often provided a square or rectangular cross-sectional profile to facilitate assembly and packing within square or rectangular modularized sections. Such cross-sectional geometry can preclude application of honeycomb SCR catalyst bodies in a variety of fields.